Hydraulic hybrid vehicle with large-ratio shift transmission and method of operation thereof

ABSTRACT

A vehicle includes an internal combustion engine configured to power a hydraulic pump to pressurize hydraulic fluid, which is used to power the vehicle directly or is stored in an accumulator. A drive module, including a hydraulic pump/motor and a multi-speed mechanical transmission, is operatively coupled to drive wheels of the vehicle to provide motive power to the vehicle. The drive module can also include a second hydraulic motor (or multiple hydraulic motors) configured to provide motive power. The transmission is configured to progress through its gears at ratio shifts of no less than 2:1 between adjacent gear positions. The transmission is configured to place the hydraulic motor in neutral during some portions of vehicle operation, and to engage the motor during other portions of vehicle operation.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/155,283, “Hydraulic Hybrid Vehicle With Large-Ratio ShiftTransmission and Method of Operation Thereof,” filed Jun. 7, 2011, nowpending, which is a continuation of U.S. patent application Ser. No.12/229,099, “Hydraulic Hybrid Vehicle With Integrated Hydraulic DriveModule and Four-Wheel-Drive, and Method of Operation Thereof,” filedAug. 19, 2008, now issued as U.S. Pat. No. 7,984,783, which is adivisional of U.S. patent application Ser. No. 11/891,869, “HydraulicHybrid Vehicle With Integrated Hydraulic Drive Module andFour-Wheel-Drive, and Method of Operation Thereof,” filed Aug. 13, 2007,now issued as U.S. Pat. No. 7,537,075, which is a divisional of U.S.patent application Ser. No. 10/769,459, “Hydraulic Hybrid Vehicle WithIntegrated Hydraulic Drive Module and Four-Wheel-Drive, and Method ofOperation Thereof,” filed Jan. 30, 2004, now issued as U.S. Pat. No.7,337,869, which is a continuation-in-part of U.S. patent applicationSer. No. 10/620,726, “Opposing Pump/Motors,” filed Jul. 15, 2003, nowissued as U.S. Pat. No. 7,374,005, which is a continuation-in-part ofU.S. patent application Ser. No. 09/479,844, “Hydraulic Hybrid Vehicle,”filed Jan. 10, 2000, now issued as U.S. Pat. No. 6,719,080, all of whichapplications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application is directed to hydraulic hybrid vehicle technology, andin particular to a drive system thereof.

2. Description of the Related Art

Significant interest has been generated, in recent years, in hybridvehicle technology as a way to improve fuel economy and reduce theenvironmental impact of the large number of vehicles in operation. Theterm hybrid is used in reference to vehicles employing two or more powersources to provide motive energy to the vehicle. For example, hybridelectric vehicles are currently available that employ an internalcombustion engine to provide power to a generator, which then generateselectricity to be stored in a battery or storage cells. This storedpower is then used, as necessary, to drive an electric motor coupled tothe drive train of the vehicle.

There is also interest in the development of hybrid hydraulic vehicles,due to the potential for greater fuel economy, and a lower environmentalimpact than hybrid electric vehicles. Inasmuch as the present inventionis directed to innovations and improvements in hybrid hydraulictechnology, where reference is made to hybrid vehicles, or hybridtechnology, it may be assumed that the reference is directed tohydraulic hybrids in particular, unless otherwise noted.

Hybrid vehicles may be grouped into two general classes, namely,parallel hybrid and series hybrid vehicles. Parallel hybrid vehicles arevehicles employing a more or less typical engine, transmission, anddrive train, with hydraulic components operating alongside. For example,FIG. 1 shows what is commonly referred to as a launch assisted vehicle100. The vehicle 100, shown in wire-frame to illustrate selectedcomponents, includes an internal combustion engine 102, a transmission104, a drive shaft 106, differential 108, drive axle 110, and drivewheels 112, as may be found in conventional vehicles. However, thevehicle 100 also includes a hydraulic pump/motor 114, in this casecoupled to the drive shaft 106, and high and low pressure hydraulicaccumulators 116, 118.

A hydraulic pump/motor is a device that functions as a motor when fluidfrom a high-pressure fluid source is used to impart rotational force toan output shaft. On the other hand, if rotational force is applied froman external source to rotate the shaft, the device may be used as apump, to pump fluid from a low pressure fluid source to high pressure.

During normal operation, the vehicle 100 operates in a manner similar toconventional vehicles. However, when the vehicle operator applies thebrake, the pump/motor 114 is coupled to the drive shaft 106 such thatrotation of the drive shaft 106 provides energy to draw fluid from thelow pressure accumulator 118 and pump the fluid at high pressure to thehigh pressure accumulator 116. Engagement of the pump/motor 114 in thismanner creates drag on the drive shaft, which is transferred to thedrive wheels 112, slowing the vehicle 100. In this way, a portion ofkinetic energy of the moving vehicle is recovered and stored ashydraulic fluid under pressure. When the vehicle 100 is pulling awayfrom a stop, or accelerating, the pump/motor 114 is again coupled to thedrive shaft 106, while the pump/motor 114 is switched to motor mode, inwhich pressurized fluid drives the pump/motor 114, which in turn addsrotational energy, or torque, to the drive shaft 106. In this way, thepump/motor is utilized in these two modes such that energy that wouldotherwise be lost to friction in the brakes of the vehicle is stored, tobe released later to assist the vehicle 100 in accelerating.

According to another parallel hybrid scheme, the engine of a vehicle isused to drive a pump to pump fluid at high pressure into an accumulator.This is done during periods when the vehicle is cruising at a steadyspeed, or otherwise demanding less than the engine is capable ofproviding when operating at its most efficient load.

It is known that internal combustion engines used in motor vehicles arerequired to have a maximum output capacity that far exceeds the averagerequirements of the vehicle, inasmuch as such vehicles occasionallyrequire power output levels far exceeding the average power output. Forexample, during acceleration from a stop, or for passing, etc., muchmore power is required than during periods when the vehicle is cruisingat a steady speed.

By using excess capacity of the engine to drive the fluid pump, the loadon the engine can be increased to a point where the engine operates at ahigh level of fuel efficiency, while the excess energy is stored aspressurized fluid. Again, the energy stored as pressurized fluid maythen be used to supplement the engine during periods when powerrequirements of the vehicle exceed the engine's maximum efficientoutput. This scheme may be implemented using a configuration similar tothat shown in FIG. 1, in which the single pump/motor 114 is used toprovide all the pumping and motoring function, or a second hydraulicpump may be provided, which is configured solely to be coupled to theengine 102 for the purpose of pumping fluid to the high pressureaccumulator 116.

Other parallel hybrid configurations are also known in the art, and willnot be discussed in detail here.

Series hybrid vehicles have no direct mechanical link between the engineand the drive wheels of the vehicle. They do not employ a transmissionor drive shaft as described with reference to parallel hybrid vehicles.In a series hybrid vehicle, a hydraulic pump is coupled directly to thecrankshaft of the engine of the vehicle. All of the energy output of theengine is used to pump fluid from a low pressure accumulator to a highpressure accumulator. A second pump/motor is coupled to the drive wheelsof the vehicle, and is driven by pressurized fluid from the highpressure accumulator. In such a vehicle, the engine may be operated witha load, and at a speed selected to provide maximum efficiency and fueleconomy, without regard to the constantly varying speed of the vehicleitself.

The configuration and operation of parallel and series hybrid vehiclesare described in detail in the following references: U.S. Pat. No.5,887,674, U.S. patent application Ser. No. 09/479,844, and U.S. patentapplication Ser. No. 10/386,029, all of which are incorporated herein byreference, in their entirety.

Although hydraulic drive equipment has been used on commercial andoff-road equipment and mobile devices for many years, hydraulic driveequipment has not yet found successful commercial application foron-road, private and multi-passenger vehicles as part of a “hybrid”powertrain. Such lack of implementation of hydraulic drive equipment inpassenger vehicles has thus far prevailed in the prior art despite thetremendous fuel economy benefits that could be obtained for suchvehicles through use of a hydraulic hybrid powertrain. As is known inthe art, a principal obstacle to implementation of hydraulic driveequipment in passenger vehicles as a hybrid powertrain is the challengeof packaging the added hydraulic equipment (e.g., pump(s), motor(s),accumulators, hoses) in addition to conventional drivetrain components(e.g., engine, transmission, differential, etc.) into the very limitedspace generally available to such components in conventional passengervehicle frames and styles. Furthermore, the increase in cost and weightcreated by the addition of hydraulic equipment to the conventionaldrivetrain components in such vehicles somewhat offsets the benefits ofa hydraulic hybrid drivetrain, by reducing the fuel economy benefits ofthe technology (due to increased vehicle weight) while simultaneouslyincreasing vehicle cost.

BRIEF SUMMARY OF THE INVENTION

According to the principles of the invention, the obstacles in the priorart are alleviated, by reducing the size, weight and/or number ofoverall components required for creation of a commercially acceptablehydraulic hybrid drive passenger vehicle, and thereby allow packaging ina passenger vehicle, at a reduced weight and cost.

According to an embodiment of the invention, an integrated drive module,for providing motive power to a vehicle, is provided, having a machinecasing, within which a hydraulic motor is enclosed, configured toconvert energy in the form of pressurized fluid, to energy in the formof torque applied to an output shaft of the motor. A differential, alsoenclosed within the casing, is coupled to the output shaft of the motorand configured to distribute the torque to right and left drive axlesegments. The drive module may also include a multi-speed transmissionenclosed within the casing and coupled between the output shaft and thedifferential.

According to another embodiment of the invention, the integrated drivemodule is configured to provide regenerative braking, by placing thehydraulic motor in a pump configuration to use torque at the drive axlesegments to pressurize fluid.

According to another embodiment of the invention, a vehicle is provided,having a plurality of axles, with each axle having a plurality of wheelscoupled thereto. The vehicle also includes an integrated drive modulecoupled to one of the plurality of axles. The module includes ahydraulic motor configured to provide motive power at an output shaftthereof, and a differential coupled to the output shaft and configuredto distribute the motive power to right and left portions of the axle.The first hydraulic motor and the first differential are encased withina common housing.

According to another embodiment of the invention, the vehicle includes asecond integrated drive module having, within a housing, a hydraulicmotor and a differential coupled to the motor and configured todistribute motive power to right and left portions of a second one ofthe plurality of axles. The second module may also include atransmission within the same housing. The second module may beconfigured to operate in a neutral mode while a power demand is below aselected threshold, and to operate in an active mode, providing motivepower to the second axle, while the power demand exceeds the selectedthreshold. Alternatively, the second module may be configured to operatein the active mode regardless of the power demand relative to theselected threshold.

According to an additional embodiment of the invention, a method forachieving a smooth transition between a 1:1 gear ratio and a high gearratio (e.g., 3:1) with just one transmission step change is provided.The method includes sensing an increase in demand for motive power froma vehicle, applying an increased amount of torque from a hydraulic motorto an output shaft of the motor, responsive to the increased demand formotive power, transmitting the torque from the output shaft of thehydraulic motor to a differential through an operatively connectedmulti-speed transmission engaged in a first gear ratio, and distributingthe torque to right and left drive axle segments of the vehicle throughthe differential, the differential being enclosed within a commonhousing with the hydraulic motor and multi-speed transmission, and thehousing being attached to the vehicle.

The method also includes destroking the hydraulic motor for a selectedtime interval to temporarily reduce the amount of torque supplied by thehydraulic motor during that time interval, changing the gear ratio ofthe multi-speed transmission from the first gear ratio to a second gearratio in conjunction with the time interval, and restroking thehydraulic motor to again increase the amount of torque supplied by thehydraulic motor responsive to a continued demand for motive power fromthe vehicle.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 shows a vehicle with a launch assist system, according to knownart.

FIG. 2 shows, in cross section, an integrated drive module, according toan embodiment of the invention.

FIG. 3 shows, in cross section, an integrated drive module, according toanother embodiment of the invention.

FIG. 4 shows, diagrammatically, a system according to an embodiment ofthe invention.

FIG. 5 shows, in cross section, an integrated drive module, according toanother embodiment of the invention.

FIG. 6 shows a portion of a truck chassis, rear axle assembly, and adrive module according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

It will be recognized that a hydraulic hybrid vehicle uses severalcomponents that are not found in a conventional vehicle. For example,such vehicles employ at least one, and frequently two or more,pump/motors. In addition, high and low pressure accumulators are used,as well as switching valves and plumbing. Offsetting this additionalequipment, in some cases, is the elimination of a drive shaft and atransmission. Nevertheless, it will be recognized that any reduction inweight will result in improved fuel economy.

FIG. 2 illustrates the principles of the invention, according to a firstembodiment. As illustrated in FIG. 2, a pump/motor 124 and adifferential 126 are incorporated into a common housing 122. The housing122 includes a differential cover 123, a pump/motor cover 125, and asupport frame 127. The output shaft 128 of the pump/motor carries adrive gear 132. The drive gear 132 directly engages the ring gear 130 ofthe differential 126, which is coupled to right and left segments 129,131 of a vehicle axle.

By incorporating the pump/motor 124 and the differential 126 within acommon housing, several advantages are realized. First, the casing 122of the integrated pump/motor/differential module 120 weighs less thanthe combined casings of a conventional pump/motor and differential.Second, by incorporating a common support frame 127, the couplingbetween the pump/motor 124 and differential 126 is more secure and rigidthan would be the case given a more conventional coupling. Third,because the drive gear 132 on the output shaft 128 directly engages thering gear 130 of the differential 126, there is no need for a separateinput or pinion shaft for the differential 126. Fourth, the hydraulicfluid that powers and lubricates the pump/motor may also providelubrication for the differential. Finally, because the coupling betweenthe pump/motor 124 and the differential 126 is very short and direct,intermediate coupling mechanisms, such as drive shafts, universaljoints, or gears are also eliminated, thus further reducing weight andvolume, and eliminating drag that might be contributed by these couplingcomponents.

The term “passenger vehicle,” as used in this specification, may beunderstood to refer to a vehicle configured to carry a driver, oroperator, and at least one passenger. The term “on-road passengervehicle” refers in particular to passenger vehicles designed principallyfor on-road use, including for use in urban areas, thus distinguishingsuch vehicles from vehicles designed principally for low-speed off-roaduse, such as e.g., tractors and other farm, construction, and miningequipment.

In designing a transmission and shifting scheme for operation of apassenger vehicle, one must pay attention to various objectives andrequirements for the design. For example, one primary objective in thedesign is to acceptably meet the high load, low speed performancerequirements of the vehicle (e.g., as in initial acceleration). As aresult, commercially acceptable passenger vehicles must be capable ofproviding a relatively high gear ratio, such as approximately 3:1 ormore for relatively large vehicles such as SUVs and trucks. In addition,in order to maximize fuel economy for passenger vehicles at lower loadand higher speed conditions, the transmission should, of course, alsoprovide for an approximate 1:1 direct drive gear ratio. For performanceand fuel economy objectives for the vehicle, these two respectiveforward gear ratios are generally sufficient to meet the particularobjectives at hand.

However, a third necessary design objective also comes into play, whichhas resulted in a prevailing need in the prior art for multi-speedtransmissions with more than just two forward speeds. In particular, thethird objective in designing a transmission and shifting scheme for acommercially acceptable passenger vehicle is that the transition betweengears must be smooth, without any harsh jerk felt by the driver orpassenger in shifts. For this reason, in a conventional passengervehicle, an increase in gear ratios between successive gears utilizedfor the vehicle is generally less than double the ratio for the previousgear (e.g., 1:1 to 2:1 or less), and frequently much less, to avoidunacceptable harshness in shifting. As a result, conventionalmulti-speed transmissions for passenger vehicles require more than justtwo forward speeds to obtain good driveability, mandating greatertransmission cost, size, and complexity, and decreasing the potentialfuel efficiency of the vehicle through the inability to quickly anddirectly shift between the vehicle's optimal high and low gear shiftratios.

FIG. 3 illustrates an integrated drive module 140 according to anotherembodiment of the invention. In addition to the pump/motor 124 anddifferential 126, as described with reference to FIG. 2, the drivemodule 140 includes a transmission 142.

The transmission 142 of the embodiment of FIG. 3 is a two-speedautomatic transmission of a planetary gear box type with two forwardratios and a geared neutral. Because the pump/motor 124, unlike typicalinternal combustion engines, is capable of operating in forward andreverse, it is not necessary for the transmission 142 to include areverse gear, thus reducing the necessary size of the transmission.Transmissions of other types and designs may also be incorporated,according to the principles of the invention.

For example, because the pump/motor 124 can destroke to a zerodisplacement configuration, in which no torque is contributed by thepump/motor 124 to the drive train, a geared neutral is not essential,according to the principles of the invention. The pump/motor at zerodisplacement with low pressure to each port provides an effectiveneutral with low frictional drag.

However, by providing the geared neutral in the embodiment of FIG. 3,even the minimal drag added by the pump/motor 124 is eliminated, whilein neutral. Thus, the integrated drive module 140 may be used inapplications where the module 140 is not a primary drive device, and somay be offline for extended periods. In such an application, the addedexpense and weight of the geared neutral is offset by the savings infuel economy afforded by the elimination of the drag, and the reducedwear of the pump/motor while in neutral.

In addition, the drive module 140 does not require a clutch between thepump/motor 124 and the transmission, to allow dynamic shifting from afirst gear to a second gear. During a gear shifting event the pump/motor124 is destroked to zero displacement to temporarily reduce the amountof torque supplied by the pump/motor 124 during the shifting event.Following the shift, the pump/motor 124 is restroked to the displacementneeded for the desired torque in the second gear. Since the rotatinginertia of the pump/motor 124 is similar in magnitude to that of aconventional clutch assembly for a similar size/torque drive system,simple synchronizers on the transmission gears, which are well known inthe art, may be used to allow smooth and rapid gear changes.

The pump/motor 124, differential 126, and transmission 142 areintegrated within a single housing 154, comprising several componentparts, including differential and pump/motor covers 155, 157, atransmission cover 159 and a main support frame 161. The same hydraulicfluid required for operation of the pump/motor may also be used foroperation of the transmission, as well as for lubrication of thedifferential.

As with the embodiment of FIG. 2, the embodiment depicted in FIG. 3provides the advantage of reducing size, weight, and drag as comparedwith conventional assemblies in which individual components areindependently mounted to a vehicle frame, and coupled together viaexternal mechanisms.

According to an embodiment of the invention, as illustrated in FIG. 4, avehicle 160 is provided. The vehicle 160 includes an internal combustionengine 162 coupled via a crankshaft 163 to a pump/motor 164. The engine162 is configured to drive the pump/motor 164, pumping fluid from a lowpressure accumulator 176 to a high pressure accumulator 174. A primaryintegrated drive module 182, similar to drive module 120 of FIG. 2,incorporating a pump/motor and differential, is coupled to a primarydrive axle 166 comprising first and second axle shafts 167, 169, whichare in turn coupled to respective primary drive wheels 170. A secondaryintegrated drive module 184, similar to drive module 140 of FIG. 3,incorporating a pump/motor, differential, and transmission, is coupledto a secondary drive axle 168, comprising third and fourth axle shafts171, 173, which are in turn coupled to respective secondary drive wheels172.

An electronic control unit 180 (ECU) is configured to monitor variousoperations and parameters, such as vehicle speed, engine speed, andfluid levels in each of the high and low pressure accumulators 174, 176,as well as operating parameters of the pump/motor 164 and the primaryand secondary integrated drive modules 182, 184. The ECU 180 is furtherconfigured to control fluid valves, which in turn control the operationof the pump/motor 164 and the pump/motors of the primary and secondaryintegrated drive modules 182, 184. The electronic control unit 180 mayalso be configured to monitor vehicle operating parameters such asaccelerator position, brake position, and selection lever position, theselection lever being used by a vehicle operator to select forward andreverse operation of the vehicle, for example. In addition, the ECU 180may also be configured to control the throttle position of the engine162.

Fluid connections between components are shown generally as fluidtransmission lines 177, while connections between the ECU 180 and thevarious components are shown as control lines 175. Additionally, valvecircuits are not shown. It will be recognized that in practice there maybe multiple fluid lines, data and control cables, sensors, valve blocksand other devices for proper operation of the system. Such devices arewell known in the art, and are therefore not described in detail.

The functions described as being performed by the ECU 180 do not have tobe centralized as shown, but may be shared or distributed among severalcomponents of the vehicle 160, or multiple ECU's. Additionally, some ofthe monitor and control functions described as being performed by theECU may not, in all embodiments, be electronic in nature. For example,mechanical, pneumatic, hydraulic, and chemical control and feedbacksystems may be employed. All such variations are considered to fallwithin the scope of the invention.

In operation, according to the embodiment illustrated in FIG. 4, theprimary integrated drive module 182 is sized and configured to provideadequate power to operate the vehicle 160 during normal operatingconditions. For example, when operating at a steady speed on a level, ordescending grade, the secondary drive module 184 is in a neutralconfiguration, providing no additional motive power to the vehicle 160.When the operator of the vehicle 160 requires acceleration or demands agreater output of power than the primary module 182 is capable ofproducing, the ECU 180 directs the secondary integrated drive module 184to engage and provide the necessary additional power. Based upon thespeed of the vehicle, and the power requirement, the ECU 180 may selecteither the first or the second gear of the transmission of the secondaryintegrated drive module 184.

For example, when starting from a dead stop, both drive modules 182, 184may be engaged to provide the necessary acceleration, with the secondarydrive module 184 in first gear. As the vehicle 160 accelerates andpasses through a threshold where the secondary drive module 184 operatesmore efficiently in the second gear, the ECU 180 will direct thetransmission of the secondary drive module 184 to shift into the secondgear, for continued smooth acceleration. When the vehicle 160 reaches acruising speed, and the power demand drops to within the capability ofthe primary module 182, or through a selected threshold, thetransmission of the secondary module 184 is returned to a neutralconfiguration. As previously explained, a geared neutral allows thepump/motor of the secondary drive module 184 to be taken completelyoffline, such that even the minimal drag of the fully destroked motor iseliminated.

The ECU 180 also controls the stroke angle of the pump/motors of theprimary and secondary drive modules 182, 184, selecting a stroke angleappropriate to the current demand for power, and the output capacity ofthe respective pump/motors.

During a braking operation, the ECU 180 directs the primary integrateddrive module 182 to reverse fluid flow, as described with reference tothe pump/motors in the background section, to act as a regenerativebrake, drawing fluid from the low pressure accumulator 176 and movingthat fluid at high pressure into the high pressure accumulator 174.During regenerative braking, the secondary integrated drive module maybe placed in a neutral configuration.

Because a pump/motor is capable of much greater low end torque, comparedto its maximum torque, than an internal combustion engine, it is capableof smoothly shifting between much more disparate gear ratios. Forexample, a vehicle employing a system such as that described withreference to FIG. 4 may shift between a 3:1 gear ratio and a high gearratio (e.g., 1:1) with just one transmission step change, therebyeliminating the prior art need in passenger vehicles for intermediategear ratios to smoothly effect such transitions in a commerciallyacceptable manner. In this way, the cost and complexity of atransmission may be reduced, as compared to a conventional vehicle withsimilar load and performance capabilities.

In order to effect a smooth gear change, the ECU 180 destrokes thepump/motor of the secondary module 184 to zero displacement, shifts thetransmission from first to second gear, then restrokes the pump/motor toan angle selected to substantially match the level of accelerationpresent just prior to destroking. From this point, the stroke angle maybe smoothly increased to increase acceleration, based upon theaccelerator position selected by the vehicle operator.

While the principles of the invention are described and illustrated withreference to a two speed transmission, the scope of the invention is notlimited to two speed transmissions, but also includes transmissionshaving three or more speeds. For example, the principles of theinvention may be practiced to advantage in a transmission using threeforward speeds in an application that might otherwise require five, in aconventional vehicle.

It is known that internal combustion engines, while capable of meeting awide range of speeds and loads, typically have ranges of speed and loadlevels at which they operate at highest efficiency. That is to say,there are speed and load levels at which the most power is produced perunit of fuel consumed. The vehicle 160 may be configured to operate suchthat the engine 162, controlled by the ECU 180, drives the pump/motor164 within a range of efficient speeds and loads, regardless of thepower demanded by the operator of the vehicle 160. The size and capacityof the engine 162 is selected to meet or exceed the average powerrequirements of the vehicle 160, within the engine's most efficientoperating range.

Accordingly, under most conditions, the engine 162 operates within itsmost efficient range of speeds, driving the pump/motor 164 to pump fluidfrom the low pressure accumulator 176 to the high pressure accumulator174, which is then used as required to drive the vehicle 160. The ECU180 may be configured to shut down the engine 162 in the event that thehigh pressure accumulator 174 becomes fully charged, such as when thevehicle 160 is operated for an extended period at less than its averagepower consumption. Alternatively, in the event that the vehicle 160exceeds its average power requirements, the ECU 180 may be configured toadvance the throttle of the engine 162 to a speed outside its mostefficient range of operating speeds, but within its power capabilities,when the fluid level in the high pressure accumulator 174 drops below aselected threshold.

Inasmuch as the engine 162 is not required to be capable of the poweroutput levels that would be necessary to provide the short termacceleration or power demanded for normal driving conditions, the engine162 may be of significantly lower capacity than would be necessary for avehicle of similar size and power output, given a conventional powertrain. The engine 162 need only be capable of meeting, within its mostefficient range of operating speeds, the average demands of the vehicle160, while being capable of operating somewhat above those averagedemands when necessary. Thus, the size of the engine 162 may be reduced,as compared to a conventional vehicle, thereby reducing the overallweight of the vehicle, further improving fuel economy.

The ECU 180 is configured to control the stroke angle of the pump/motorsof the primary and secondary drive modules 182, 184, the selection ofthe drive gear of the transmission of the secondary drive module 184,and the power output of the engine 162, based upon selected parameters.For example, the selection may be based upon maximum efficiency ofoperation, for the purpose of optimizing fuel economy and reducingemissions. Alternatively, the selection may be based upon best possiblepower output, for use in high performance vehicles. In another case, theselection may be based upon a requirement to minimize wear on thecomponents of the system, or on a particular one of the components. Thedecisions made by the ECU 180 in controlling the various parameters ofthe system, and selecting thresholds for particular events, may be madeusing a variety of tools. For example, real time calculations based onsensor inputs, look-up tables, pre-established limits, and combinationsof the above, may all be employed.

According to an embodiment of the invention, a manual override isprovided, such that a vehicle operator may engage the secondary drivemodule full time, for four-wheel-drive operation. Unlike conventionalfour-wheel-drive vehicles, the vehicle 160 of FIG. 4 does not require adifferential between the front and rear axles, further reducing the massand complexity of the vehicle 160, as compared to a conventionalvehicle. Thus, in addition to use in passenger vehicles and light dutytrucks, the system described with reference to FIG. 4 is ideal for usein light sport-utility and off-road vehicles.

FIG. 5 illustrates an integrated drive module 190 according to anotherembodiment of the invention. The integrated drive module 190 includesfirst and second opposing pump/motors 192, 194, two-speed transmission196, and differential 198 (details of the differential are not shown).The integrated drive module 190 includes a casing 200, configured toenclose the various components thereof in a manner similar to thatdescribed with reference to previous embodiments.

The opposing pump/motors 192, 194 are configured to operate in tandem,namely, they are coupled together such that the stroke angle of eachpump/motor 192, 194 is substantially equal to that of the other. Thus,axial forces generated within each pump/motor are largely canceled bythose generated by the opposite pump/motor. A detailed description ofthe structure and operation of opposing pump/motors of the typeillustrated in FIG. 5 may be found in U.S. patent application Ser. No.10/620,726, which is incorporated herein by reference, in its entirety.

One advantage of opposing pump/motors such as those shown in theembodiment illustrated in FIG. 5, is that, for a total given maximumdisplacement, two synchronized pump/motors in opposition, such as thoseshown in the drive module 190 of FIG. 5, have a lower total mass andsize than would a single pump/motor having an equivalent maximumdisplacement. Accordingly, an application requiring a greater maximumpower output than can be provided by drive modules of previouslydescribed embodiments may employ the drive module 190 of FIG. 5, which,given an equal, or slightly greater mass, is capable of a much highermaximum output.

One application of the integrated drive module 190 of FIG. 5, is in avehicle such as that described with reference to FIG. 4, in place of thesecondary drive module 184, where the vehicle is a medium duty vehiclerequiring a greater maximum output, such as a larger sport-utilityvehicle or truck.

FIG. 6 illustrates an integrated drive module 210 and rear axle assembly212 of a vehicle according to another embodiment of the invention.Integrated Drive module 210 includes first, second, and thirdpump/motors 214, 216, 218, and differential 220. The differential 220 iscoupled to first and second axle shafts 222, 224, which are in turncoupled to drive wheels 226.

Functionally, the integrated drive module 210 operates in a mannersimilar to a combination of the primary and secondary integrated drivemodules 182, 184, as described with reference to FIG. 4. For example, ifthe vehicle associated with the integrated drive module 210 and rearaxle assembly 212 is cruising at a fixed speed, only the pump/motor 218may be engaged and providing motive power to the vehicle, while thefirst and second pump/motor 214, 216 remain in a neutral configuration.Alternatively, when additional power is required, such as foracceleration or for climbing an incline, the first and secondpump/motors 214, 216 are engaged to provide additional motive force, asrequired. It may be seen that, in the configuration illustrated in FIG.6, the first and second pump/motors 214, 216 are in an opposingconfiguration, similar to that described with reference to theintegrated drive module 190 of FIG. 5, and so enjoy similar advantages.

The integrated drive module 210 may be advantageously employed toprovide motive power to larger vehicles, such as larger trucks or stepvans of the type used for collecting and distributing freight items inurban areas, trucks used to collect refuse, tow trucks, and other largevehicles employed in urban environments.

It will be recognized that, while the various embodiments of theinvention have been described with reference to a yoked bent-axispump/motor, there is a wide variety of pump/motor types that may be usedin connection with the embodiments of the invention. For example, othertypes of pump/motors include the sliding valve plate bent-axispump/motor, the swash plate pump/motor, the wobble plate pistonpump/motor, and the radial piston pump/motor. These and other hydraulicmotor devices are considered to fall within the scope of the invention.

The term adjacent, where used to refer, in a transmission, to gears,speeds, gear ratios or the like, refers in particular to pairs of gearcombinations in the transmission that would follow one another insequence when all of the gear combinations of the transmission areordered according to their respective ratios.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

1. A drive module of a vehicle, comprising: a support frame; a firsthydraulic pump/motor coupled to the support frame and having a firstdriveshaft; a second hydraulic pump/motor coupled to the support frameand having a second driveshaft rotationally coupled to the firstdriveshaft; and a mechanical transmission coupled to the support frameand operatively coupled to the first and second hydraulic pump/motorsfor selective transmission of rotational force from the first and seconddriveshafts to a differential of the vehicle at a ratio that isselectable from among a plurality of ratios, no change of ratios betweenany two successive gear ratios of the transmission being less than 2:1.2. The module of claim 1 wherein no change of ratios between any twosuccessive gear ratios of the transmission is less than 3:1.
 3. Themodule of claim 1 wherein the transmission is configured to place thefirst and second pump/motors in a neutral condition relative to thedifferential while a separate power source provides motive power to thevehicle.
 4. The module of claim 3 comprising a third hydraulicpump/motor operatively coupled to the differential and configured to actas the separate power source.
 5. The drive module of claim 1 wherein thedrive module is integrated into a housing having separate covers foreach of the first and second pump/motors and the transmission.
 6. Thedrive module of claim 1, comprising a differential coupled to thesupport frame and operatively coupled to the transmission to receiverotational force from the transmission and to distribute the rotationalforce to first and second wheels of the vehicle.
 7. A drive system for ahybrid vehicle, comprising: a first power source, including a firstpump/motor having a first driveshaft; a second power source, including asecond pump/motor having a second driveshaft rotationally coupled to thefirst driveshaft so as to rotate at a common rate with the firstdriveshaft; a third pump/motor configured to be powered to pressurizefluid for driving the first and second pump/motors; a mechanicaltransmission having an input and an output, the input operativelycoupled to the first and second driveshafts, the transmission includinga neutral setting, at which the first and second pump/motors aredisengaged from the output; a third power source capable of providingmotive power to the vehicle independent of the first and second powersources.
 8. The drive system of claim 7 wherein the first and secondpump/motors and the transmission are encased within a common housing. 9.The drive system of claim 7, comprising an internal combustion engineconfigured to selectively drive the third pump/motor.
 10. The drivesystem of claim 9 wherein a driveshaft of the third pump/motor isoperatively coupled to a driveshaft of the engine.
 11. The drive systemof claim 7 wherein the first and second driveshafts are coupled to theinput of the transmission without an intervening clutch.
 12. The drivesystem of claim 7 wherein the third power source includes a fourthpump/motor.
 13. The drive system of claim 7 wherein the output of themechanical transmission and the third power source are both operativelycoupled to a pair of drive wheels.
 14. The drive system of claim 7wherein the output of the mechanical transmission is operatively coupledto a first pair of drive wheels and the third power source isoperatively coupled to a second pair of drive wheels.
 15. The drivesystem of claim 7 wherein the transmission comprises: a plurality ofindividually selectable gear ratios; and a synchronizer configured tosynchronize a rotation speed of the first and second driveshafts with arotation speed of the output of the transmission according to a ratio ofone of the plurality of gear ratios.
 16. The drive system of claim 7wherein the transmission includes a plurality of individually selectablegear ratios between the input and the output, and wherein a differencein ratio between any one of the gear ratios and any adjacent one of thegear ratios is at least 2:1.
 17. The drive system of claim 16 whereinthe difference in ratio between any one of the gear ratios and anyadjacent one of the gear ratios is at least 3:1.
 18. The drive system ofclaim 7 comprising a control unit configured to control changes ofdisplacement of the first and second pump/motors so that the respectivedisplacements change substantially simultaneously and remainsubstantially equal to each other.
 19. The drive system of claim 7wherein the first and second pump/motors are positioned in opposition toeach other so that axial forces acting on the driveshafts of therespective pump/motors substantially cancel.
 20. A method for operatinga hybrid vehicle, comprising: accelerating the hybrid vehicle byapplying high-pressure fluid to a hydraulic machine coupled to applytorque to a drive axle of the vehicle; removing torque applied by thehydraulic machine by reducing a fluid displacement of the machine;following the removing torque, changing from a first gear ratio to asecond gear ratio of a transmission interposed between the hydraulicmachine and the drive axle, a difference in ratio between the first gearratio and the second gear ratio being at least 2:1; and following thechanging from a first gear ratio to a second gear ratio, restoringtorque applied by the hydraulic machine by increasing the fluiddisplacement of the machine.
 21. The method of claim 17 wherein thedifference in ratio between the first gear ratio and the second gearratio is at least 3:1
 22. The method of claim 20 wherein the restoringtorque comprises increasing torque, immediately following the changingfrom a first gear ratio to a second gear ratio, until an accelerationlevel of the vehicle is substantially equal to an acceleration level ofthe vehicle immediately prior to the removing torque.
 23. The method ofclaim 20, comprising: shifting the transmission to place the hydraulicmachine in a neutral condition while the vehicle is traveling at asubstantially constant cruising speed; and providing motive power to thevehicle from a separate power source while the hydraulic machine is in aneutral condition.
 24. The method of claim 20, comprising: movingpressurized fluid to a hydraulic accumulator by operating an internalcombustion engine to power a hydraulic pump.
 25. The method of claim 20,comprising: operating the hybrid vehicle in a reverse direction byreversing a direction of torque applied by the hydraulic motor to thedrive axle.
 26. The method of claim 20 wherein: the hydraulic machinecomprises a pair of hydraulic machines coupled together and configuredto rotate at an equal rate; applying high-pressure fluid to thehydraulic machine comprises applying hydraulic fluid to the pair ofhydraulic machines; reducing the fluid displacement of the hydraulicmachine comprises reducing the fluid displacement of each of the pair ofhydraulic machine substantially equally; and increasing the fluiddisplacement of the hydraulic machine comprises increasing the fluiddisplacement of each of the pair of hydraulic machine substantiallyequally.
 27. The method of claim 20 wherein the method is a method foroperating an on-road passenger hybrid vehicle.